Effects of nanocrystalline CeO 2 supports on the properties and performance of Ni–Rh bimetallic catalyst for oxidative steam reforming of ethanol

Abstract

This study focuses on the effects of the CeO 2 support properties on the catalyst properties and performance of bimetallic Ni–Rh/CeO 2 catalysts containing 5 wt% Ni and 1 wt% Rh for the oxidative steam reforming (OSR) of ethanol for hydrogen production and fuel cell applications. Three CeO 2 supports with different crystal sizes and surface areas were examined. The surface areas of these supports increases in the order of CeO 2-I (74 m 2/g) < CeO 2-II (92 m 2/g) < CeO 2-III (154 m 2/g), but their crystallite sizes were about 10.2, 29.3, and 6.5 nm, respectively. The properties of Ni–Rh/CeO 2 catalysts were investigated by XRD, TPR, H 2 chemisorption, and in situ XPS techniques. The Rh metal dispersion increased while the Ni metal dispersion decreased with decreasing crystallite sizes of CeO 2. TPR studies revealed the existence of a Rh–CeO 2 metal–support interaction as well as Ni–Rh interaction in the Ni–Rh bimetallic catalyst supported on CeO 2-III with a crystallite size of about 6.5 nm. The in situ XPS studies corroborated the TPR results. The reduced Ni and Rh species were reversibly oxidized, suggesting the existence of Ni–Rh redox species rather than NiRh surface alloy in the present catalyst system. The Rh species became highly dispersed when the crystallite size of CeO 2 support was smaller. Comparing the catalytic performance in the OSR of ethanol with the properties of the catalysts demonstrated that both ethanol conversion and H 2 selectivity increased and the selectivity for undesirable byproducts decreased with increasing Rh metal dispersion. Best catalytic performance for OSR was achieved by supporting Ni–Rh bimetallic catalysts on the nanocrystalline CeO 2-III. The Ni–Rh/CeO 2-III catalyst exhibited stable activity and selectivity during on-stream operations at 450 °C and as well as at 600 °C.